Vacuum contactors are utilized as switching or circuit-breaking mechanisms for a variety of alternating current (AC) loads such as three-phase motors, transformers, power distribution switchgear, surge suppression circuits, power capacitors and resistive heating loads. The vacuum contactor may be found in medium voltage power circuit applications ranging up to about 38 kV.
A vacuum contactor typically comprises a number of vacuum interrupters equal to the number of electrical phases and an actuating mechanism for the control thereof. The vacuum interrupter is a vacuum tight bottle in which a pair of contacts is enclosed. One of the contacts is fixed to one end of the bottle and the other contact is movable. The movable contact has a movable stem extending from the other end of the bottle and is sealed thereto by means of a bellows. The bellows allows the movable contact to reciprocate between a closed position wherein the movable contact abuts the fixed contact and an open position wherein the movable contact is spaced apart from the fixed contact at a distance sufficient to prevent arcing at a given breakdown voltage. If the contacts are separated while alternating current is flowing an arc will be formed which begins to vaporize the contact faces. This forms a charged vapour which is collected on a shield disposed within the bottle. However, as the alternating current reaches a zero magnitude the arc will extinguish and, because the rapid dispersion of the vapour leaves no charged medium in the vacuum, the arc will be unable to re-establish itself between the open contacts.
Since the vacuum interrupters encase their contacts within a vacuum, the normal, unbiased, position of a vacuum interrupter is the closed position. Some sort of biasing means, such as a spring-loaded solenoid as discussed in greater detail below, is typically employed to bias the vacuum interrupter in the open position, and to close the vacuum interrupters upon command.
An example of a typical three-phase vacuum contactor 10 is described with reference to FIGS. 1 and 2 which show front and cross sectional views thereof. As shown, the contactor 10 comprises three vacuum interrupters 12 arranged in a single row along the same plane and fixed to a casing 14. Each vacuum interrupter 12 has a moveable shaft or stem 22 for opening and closing the vacuum interrupter. These shafts are surrounded by electrical insulators 26. An electromagnetic actuating device 16 is disposed below the row of vacuum interrupters 12 and is orientated normal to the plane in which the vacuum interrupters lie. The actuator 16 features an armature 18 that is connected to an L-shaped mechanical linkage 20 which, in turn, is pivotably linked to the movable shafts or stems 22 of the vacuum interrupter. A spring 24 is attached to the casing 14 and provided to bias the mechanical linkage 20 and the vacuum interrupters 12 in the open position, as shown in FIG. 2 wherein the mechanical linkage 20 abuts against a stop 26. A second spring 28 is disposed about each moveable shaft or stem 22 between the mechanical linkage 20 and the elecrical insulator 26. To close the vacuum interrupters 12 the actuator 16 must be energized, causing the mechanical linkage 20 to compress springs 24 and 28 as well as the moveable shafts or stems 22 of the vacuum interrupters. It will thus been seen that the stroke of the electromagnetic actuating device 16 is orientated perpendicular to the strokes of the vacuum interrupters 12. This design, while durable and proven in the field, is overly bulky.
While prior art multiphase contactors such as the one described above have proved useful and durable in a wide range of applications, mechanically, they are rather bulky. The invention therefore seeks to provide vacuum contactors capable of occupying minimal space envelopes.